This invention relates generally to intrinsically safe power supply systems, and more particularly, to a power supply arrangement wherein rectified DC current is periodically interrupted by a clock-controlled semiconductor device connected in series with a primary winding of a transformer; the output of the power supply being provided at a secondary winding of the transformer which is provided with a regulator for limiting the output current and a shorting switch controlled in response to predetermined limits.
A power supply arrangement of the type described above is described in German Reference No. DE-A-28 43 093. The known power supply described in this reference is provided with multiply-redundant current and voltage limitations, and satisfies the stringent safety requirements of category "ia" of the European Standard No. EN 50020. This standard is met even though controlled semiconductors are used for limiting the current. This known power supply arrangement, however, operates with a relatively large dissipation loss which produces an undesirable temperature rise in the equipment. Moreover, such a temperature rise presents considerable difficulties in achieving theoretically approximated limits for protective currents and voltages.
It is, therefore, an object of this invention to achieve as nearly as possible the utilization of the power supply at the theoretical limits of intrinsical safety (UL-Standard No. 973, 3.8).
It is a further object of this invention to achieve such maximum utilization with load dissipation and with simple and inexpensive circuit design.